The present invention relates to a motor-driven compressor including a housing, a compression mechanism accommodated in the housing and an electric motor configured to drive the compression mechanism and also to an air conditioner in which the motor-driven compressor is connected.
Japanese Patent Application Publication No. 8-258548 discloses a heat pump system in which a motor-driven compressor forming a part of refrigeration cycle is applied to a heat pump for heating. Referring to FIG. 5 showing a refrigerant circuit in a heat pump system 80 according to a background art, refrigerant discharged from the motor-driven compressor 81 of the heat pump system 80 is flowed through the selector valve 82 to the outside heat exchanger 83, as indicated by dotted arrow Y1, where the refrigerant is condensed. Then, the refrigerant is decompressed by the expansion valve 84 and evaporated in the inside heat exchanger 85, thus cooling of an interior space being accomplished by the air cooled by the evaporation. Then, the refrigerant is flowed through the selector valve 82 and the accumulator 86 and returned to the motor-driven compressor 81.
During heating operation of the system, on the other hand, refrigerant discharged from the motor-driven compressor 81 is flowed through the selector valve 82 and condensed by the inside heat exchanger 85, as indicated by solid arrow Y2. Heating of the interior space is accomplished by the air heated by the heat exchange in the inside heat exchanger 85. Then, the refrigerant is decompressed by the expansion valve 84, evaporated by the outside heat exchanger 83, flowed through the selector valve 82 and the accumulator 86 and returned to the motor-driven compressor 81.
According to the above-cited Publication, when the motor-driven compressor 81 is used in a heat pump for heating, refrigerant discharged from the motor-driven compressor 81 causes discharge pulsation which is transferred to the inside heat exchanger 85 during the heating operation of the motor-driven compressor 81 (under a specific condition). The discharge pulsation transmitted to the inside heat exchanger 85 through pipes causes development of a noise in the vehicle interior. For reducing the discharge pulsation, it may be so arranged that the motor chamber doubles as a discharge chamber in the motor-driven compressor 81. In this structure wherein high-pressured compressed refrigerant is introduced into the motor chamber, however, the electric motor is hardly cooled. In the electric motor having a permanent magnet, the permanent magnet of the electric motor is hardly cooled thereby to be demagnetized, so that performance of the electric motor is deteriorated and the torque of the motor reduced. Accordingly, the performance of the electric motor is deteriorated. For reducing the discharge pulsation of refrigerant, the discharge chamber of the motor-driven compressor 81 may be formed with an increased volume. Such discharge chamber only increases the size of the motor-driven compressor 81 and affects the ease of installation of the compressor in a vehicle.
The present invention is directed to providing a motor-driven compressor configured to reduce the discharge pulsation of refrigerant under a specific condition.